1) Field of the Invention
The field of the present invention pertains to microelectronic circuit fabrication and, more particularly, to methods and apparatus for controlling microelectronic circuit fabrication processes.
2) Background
The quality of microelectronic circuits and/or components, such as those manufactured from a semiconductor wafer, is directly dependent on the consistency of the processes used in its fabrication. More particularly, production of such circuits and/or components requires reproducible etching, deposition, diffusion, and cleaning processes. A failure to maintain control of the processes within defined manufacturing tolerances results in decreased yield and decreased profitability for a fabrication facility.
In a typical scenario, the manufacturing process exhibits slow drifts that change the batch-to-batch properties of the product. Very often, these effects are due to slight variations in the operation of one or more processing tools over the time in which the different batches are processed. Additionally, in large scale operations, the same processing operation may be executed on a plurality of processing tools of the same type to process parallel batches of the product. The same processing recipe is generally used to concurrently control the operations of the plurality of similar processing tools. However, minor variations in the way in which an individual tool responds to the recipe parameters to execute the process can drastically affect the resulting product performance when compared with products processed on other ones of the similar processing tools.
Traditionally, this problem has been handled manually by a human operator, using statistical process control (SPC) concepts. More particularly, a human operator monitors the product output as the result of the execution of a process recipe on a particular tool and tweaks the recipe for subsequent product runs. In many instances, however, the process recipes can number in the hundreds. As such, monitoring and manually adjusting these recipes for process drift can be very time consuming, error prone and lacking in accuracy.
A common methodology for monitoring batch processes utilizes x-bar/s or x-bar/r plots in commercial or internally developed SPC software packages. Normally, distributed process data is typically monitored automatically utilizing a set of rules (such as Western Electric) to determine if the process is xe2x80x9cin-control.xe2x80x9d Manual investigation and adjustment of the process is necessary once a data point is determined to be out of control. A large percentage of these adjustments are made to compensate for the run-to-run variations attributed to process equipment drift. Unfortunately, there are many problems using manually adjusted processes based on SPC charts. A typical wafer fabrication plant may have about 2,500 on-line SPC charts. If all of the Western Electric rules were used, and if just two new points were added to each chart per day, it is estimated that there would be on average 82 false alarms per day. Due to the sheer magnitude of faults that are reported in such circumstances, only the processes with the most significant excursions tend to be maintained. In some cases, however, the opposite is true, and too much attention is given to a chart, leading to over-adjustment of data points which in turn results in processes xe2x80x9cringing.xe2x80x9d Additional process variation can be introduced between shifts or individuals as they all try to compensate for each other""s process adjustments, compounding the problem.
The present inventors have recognized the foregoing problems and have developed an advanced run-to-run controller suitable for use in a microelectronic fabrication facility.
The invention provides in one aspect an advanced run-to-run controller for use in microelectronic fabrication.
In one embodiment, an advanced run-to-run controller for controlling manufacturing processes comprises set of processing tools, a set of metrology tools for taking metrology measurements from the processing tools, and a supervising station for managing and controlling the processing tools. The supervising station comprises an interface for receiving metrology data from the metrology tools and a number of variable parameter tables, one for each of the processing tools, collectively associated with a manufacturing process recipe. The supervising station also includes one or more internal models which relate received metrology data to one or more variables for a processing tool, and which can modify variables stored in the variable parameter table to control the process tools using feedback and/or feed-forward control algorithms. Feed-forward control algorithms may, in certain embodiments, be used to adjust process targets for closed loop feedback control.
In a preferred embodiment, the supervising station has a user interface by which different feedback or feed-forward model formats (single or multi-variate) may be interactively selected based upon experimental or predicted behavior of the system. The supervising station may also permit users to utilize their own models for run-to-run control.
Further variations, modifications and alternative embodiments are also described herein.